While a laser beam propagated in all directions is required, there is no apparatus for generating the laser beam up to now. It is expected that the apparatus for generating the laser beam propagated in all directions is applied to a variety of applications if the apparatus could be realized. One of the applications is a security system. For security of a wide space, a plurality of devices of generating laser beams traveling straight should be installed at present. However, if there exists a device of generating a plane beam or a conical beam, which is provided by the present invention, the wide space can be easily monitored only with a small number of laser beam generating devices.
Security becomes increasingly important in these days. For instance, it is difficult to prevent an intruder who attempts to access a building or other security areas. As a technique of protecting the security areas is developed, attempts to break a security system become diversified. Accordingly, a system capable of detecting an intruder in the security areas is urgently required.
One of security systems is disclosed in U.S. Pat. No. 4,949,074, which projects a beam of infrared radiation and receives the radiation of the reflected beam. Furthermore, U.S. Pat. No. 3,715,953 discloses a regional security and fire prevention system including a laser range finder. However, this system has a small security area because the security area is limited to a range in which a laser beam is projected and returned. Thus, a plurality of laser beams traveling straight should be used in order to widen the security area.
U.S. Pat. No. 4,939,379 discloses a system that scans the surface of a target and measures the contour of the surface. However, this system requires a device of rotating a laser beam because it scans the entire security area with the laser beam. One of intrusion detection systems is disclosed in U.S. Pat. No. 5,365,218. The disclosed system includes a laser device set in a rotating apparatus and needs a motor for rotating the laser device to scan a security area and other components for the rotation. This increases the volume and cost of the security system and makes maintenance of the system difficult.